public class MyLinkedList {
    static class ListNode {
        public int val;
        public ListNode prev;
        public ListNode next;

        public ListNode(int val) {
            this.val = val;
        }
    }
    public ListNode head;//标记双向链表的头部
    public ListNode tail;//标记双向链表的尾部
    public int size(){
        ListNode cur = head;
        int count = 0;
        while(cur != null){
            count++;
            cur = cur.next;
        }
        return count ;
    }
    public void display(){
        ListNode cur = head;
        while (cur != null){
            System.out.print(cur.val+" ");
            cur = cur.next;
        }
    }
    //查找是否包含关键字key是否在单链表当中
    public boolean contains(int key){
        ListNode cur = head;
        while (cur != null){
          if(cur.val == key){
              return  true;
          }
            cur = cur.next;
        }
        return false;
    }
    //头插法
    public void addFirst(int data){
        ListNode node = new ListNode(data);
        if(this.head==null){
            this.head = node;
            this.tail = node;
        }else {
            node.next = this.head;
            this.head.prev = node;
            this.head = node;
        }
    }
    public void addLast(int data){
        ListNode node = new ListNode(data);
        if(this.head==null){
            this.head = node;
            this.tail = node;
        }else {
            this.tail.next = node;
            node.prev = this.tail;
            this.tail = node;
        }
    }
           //任意位置插入,第一个数据节点为0号下标
    public void addIndex(int index,int data) {
        //1、判断Index位置的合法性
        if (index < 0 || index > size()) {
            throw new PosIllegalEcception("index位置不合法");
        }
        //2、判断特殊位置，头插 和 尾插
        if (index == 0) {
            addFirst(data);
            return;
        }
        if (index == size()) {
            addLast(data);
            return;
        }
         //3、找到index位置节点的地址
        ListNode cur = findIndexListNode(index);
        ListNode node = new ListNode(data);
        node.next = cur;
        cur.prev.next = node;
        node.prev = cur.prev;
        cur.prev = node;
    }
          //找index位置的元素
        private ListNode findIndexListNode ( int index){
            ListNode cur = head;
            while (index != 0) {
                cur = cur.next;
                index--;
            }
            return cur;
        }

    public void remove(int key){
        ListNode cur = head;
        while (cur != null) {
            if(cur.val == key) {
                //删头节点
                if(cur == head) {
                    head = head.next;
                    if(head!=null) {
                        head.prev = null;
                        //删到只剩一个节点时
                    }else {
                        tail = null;
                    }
                }else {
                    cur.prev.next = cur.next;
                    if(cur.next != null) {
                        cur.next.prev = cur.prev;
                    }else {
                        //删尾巴节点
                        this.tail = cur.prev;
                    }
                }
                return;
            }
            cur = cur.next;
        }
    }
    //删除所有值为key的节点
    public void removeAllKey(int key){
        ListNode cur = head;
        while (cur != null) {
            if(cur.val == key) {
                //删头节点
                if(cur == head) {
                    head = head.next;
                    if(head!=null) {
                        head.prev = null;
                        //删到只剩一个节点时
                    }else {
                        tail = null;
                    }
                }else {
                    cur.prev.next = cur.next;
                    if(cur.next != null) {
                        cur.next.prev = cur.prev;
                    }else {
                        //删尾巴节点
                        this.tail = cur.prev;
                    }
                }
            }
            cur = cur.next;
        }
    }
    public void clear(){
        ListNode cur = head;
        while(cur != null ){
            ListNode curNext = cur.next;
            cur.prev = null;
            cur.next = null;
            cur = curNext;
        }
        head = null;
        tail =null;
    }
}
